Do you know how facebook defines an “active user” ? I’m curious about it.

I don’t know specifics, but I would take a guess that it means someone who has logged-in during a given period of time. What that time would be, I don’t know. It could be days or weeks.

[valleywag.com]

Well, in the US MySpace still dominates, but elsewhere Facebook seems to be more popular, as most of the Facebook users are people outside of the US.

If by dominates you mean still holds a marginal user share that is not increasing, while Facebook quickly catches up – then yes.

Well, in the US MySpace still dominates, but elsewhere Facebook seems to be more popular, as most of the Facebook users are people outside of the US.

According to Alexa 36% of Facebook’s traffic is from the U.S., and in second place is the UK with 10%. So the U.S. accounting for over a third of all the traffic means it is pretty significant.